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Inhibition by 2-Deoxy-D-Glucose of Synthesis of Saccharomyces

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Inhibition by 2-Deoxy-D-Glucose of Synthesis of Saccharomyces JOURNAL OF BACTROLOGY, Aug. 1972, p. 419-429 Vol. 111, No. 2 Copyright 0 1972 American Society for Microbiology Printed in U.S.A. Inhibition by 2-Deoxy-D-Glucose of Synthesis of Glycoprotein Enzymes by Protoplasts of Saccharomyces: Relation to Inhibition of Sugar Uptake and Metabolism' S.-C. KUO AND J. 0. LAMPEN Institute of Microbiology, Rutgers University, 7he State University of New Jersey, New Brunswick, New Jersey 08903 Received for publication 17 April 1972 The synthesis of the glycoprotein enzymes, invertase and acid phosphatase, by protoplasts of Saccharomyces mutant 1016, is inhibited by 2-deoxy-D-glu- cose (2-dG) after a 20- to 30-min lag period under conditions (external sugar to 2-dG ratio of 40:1) which cause only a slight decrease in total protein syn- thesis. Formation of one intracellular enzyme, alpha-glucosidase, is also sensi- tive, but production of another, alkaline phosphatase, is unaffected. A nonme- tabolized glucose analogue, 6-deoxy-D-glucose, had no inhibitory effect. The total uptake of external fructose and maltose was decreased by 2-dG after a lag period of about the same duration as that before the inhibition of synthesis of enzymes or of mannan and glucan; during this time 2-dG was taken up by the protoplasts and accumulated primarily as 2-dG-6-phosphate (2-dG-6-P). Studies in vitro showed that 2-dG-6-P inhibits both yeast phosphoglucose isomerase and phosphomannose isomerase. The intracellular levels of the 6- phosphates of glucose, fructose, and mannose did not increase in the presence of 2-dG. We suggest that the high internal level of 2-dG-6-P blocks synthesis of the cell wall polysaccharides and glycoproteins in two ways. It directly inhibits the conversion of fructose-6-P to glucose-6-P and to mannose-6-P. At the same time, it restricts the transport of fructose and maltose into the cell; however, the continuing limited uptake of the sugars still provides sufficient energy for protein synthesis. The cessation of alpha-glucosidase synthesis is probably a result of depletion of the internal pool of maltose (the inducer). Our findings support the suggestion that restriction of synthesis of the carbohydrate moiety of glycoproteins reduces formation of the active enzyme. 2-Deoxy-D-glucose (2-dG), a potent inhibitor (15) and Liras and Gascon (27) reported that of the growth of yeast cells and of their fer- low levels of 2-dG selectively blocked the syn- mentation of sugars, has been the subject of thesis and secretion of mannan proteins (in- many studies. Its effects have usually been at- cluding invertase) by protoplasts under condi- tributed either to interference with the en- tions in which no significant inhibition of total trance of the fermentable sugars or to preven- protein synthesis was observed. tion of the synthesis of cell wall polysaccha- This communication describes the effect of rides by trapping uridine nucleotides as uri- 2-dG on the synthesis of two extemal enzymes, dine diphosphate 2-dG or by incorporating 2- the mannan proteins, acid phosphatase (EC dG into cell wall materials (5, 18, 21). As work 3.1.3.2) and invertase (EC 3.2.1.26) (6, 25, 28) with 2-dG progresses, it is becoming obvious and on two intracellular enzymes, alkaline that the glucose analogue has multiple effects phosphatase (EC 3.1.3.1) and alpha-glucosidase on cellular metabolism. Recently, Farkas et al. (EC 3.2.1.20) (17, 19, 28, 36), and the relation- ' A preliminary report of these findings was presented at ship between the intracellular level of 2-deoxy- the IV International Fermentation Symposium, Kyoto, Ja- glucose phosphates and the impairment of pan, March 1972. sugar uptake and metabolism. We also report 419 420 KUO AND) ILAMPEN J. BACTERIOL. that 2-deoxyglucose-6-phosphate (2-dG-6-P) adding 1 ml of 1 M NaOH. Alkaline phosphatase was inhibits the conversion of fructose-6-P to glu- determined by incubating 1.6 ml of 1 M tris(hydroxy- cose-6-P and of mannose-6-P to fructose-6-P methyl)aminomethane (Tris)-hydrochloride (pH 8.9), by purified yeast phosphoglucose isomerase 0.1 ml of the test sample, and 0.3 ml of 0.04 M PNPP at 30 C; 1.0 ml of 1 M NaOH was added to (EC 5.3.1.9) and phosphomannose isomerase stop the reaction. The increase of absorbancy at 410 (EC 5.3.1.8), respectively. The implications of nm resulting from the liberation of p-nitrophenol these findings with respect to the mechanism was measured with a Beckman DB spectropho- of the inhibition by 2-dG of synthesis of cell tometer. One unit of phosphatase activity is the wall polysaccharides and glycoprotein enzymes amount of enzyme which liberates 1 Amole of nitro- by protoplasts are discussed. phenol (or Pi) per hr. Phosphoglucose isomerase was determined in a coupled enzyme assay by the conversion of fructose- MATERIALS AND METHODS 6-P to glucose-6-P, which was further converted to 6- Yeast strain, preparation of organisms, and phosphogluconic acid with glucose-6-phosphate de- protoplasts. The Saccharomyces mutant 1016 used hydrogenase and nicotinamide adenine dinucleotide in these experiments is maltose-positive. It was phosphate (NADP). The formation of NADPH was chosen because it produces a considerable amount of measured spectrometrically at 340 nm. The reaction invertase if the cells are grown on either maltose or a mixture (1.0 ml) consisted of 100,umoles of Tris-hy- low-hexose medium (24). For experiments involving drochloride buffer (pH 8.0), 1 umole of NADP, 5 ug acid and alkaline phosphatases, the cells from a 24- of glucose-6-phosphate dehydrogenase, 1 gg of yeast hr slant were transferred into 100 ml of Vogel's (40) phosphoglucose isomerase (Boehringer), and fruc- medium N with added vitamins (24) containing 0.05 tose-6-P as indicated. The experiments were con- M maltose, and were incubated for 14 to 15 hr at 28 ducted at room temperature. C on a reciprocating shaker. Protoplasts were pre- Phosphomannose isomerase was measured by the pared from these exponential-phase cells by the pro- formation of fructose-6-P from mannose-6-P. The cedure of Kuo and Lampen (24) and washed with 0.8 reaction mixture (1.0 ml) contained 100 gmoles of M sorbitol in the modified Vogel's medium N with Tris-hydrochloride buffer (pH 7.6), 0.035 Mig of yeast the phosphate omitted (0.8 M sorbitol medium) as phosphomannose isomerase (Sigma), and mannose- used by McLellan and Lampen (28). 6-P in the absence or presence of 2-dG-6-P as indi- For induction of alpha-glucosidase in the proto- cated. After incubation for 2 min at 28 C, the reac- plasts, the cells were grown in 0.2 M glucose. Proto- tion was terminated by removing 0.5 ml of sample plasts were prepared and washed with phosphate into 1.0 ml of Tris-hydrochloride buffer held at 95 C. buffer containing 0.8 M sorbitol as previously de- The amount of fructose-6-P formed was then meas- scribed (24). Alpha-glucosidase synthesis was then ured by the increase of absorbancy at 340 nm due to measured in a medium containing maltose as in- the reduction of NADP to NADPH after additions of ducer. phosphoglucose isomerase and glucose-6-phosphate Measurement of enzyme formation and secre- dehydrogenase. The results were quantitated by the tion by protoplasts. Washed protoplasts were sus- use of an intemal standard of fructose-6-P, with or pended at 5 x 101 per ml in 0.8 M sorbitol medium without 2-dG-6-P in order to correct for the slight with the indicated concentration of sugar as energy interference by 2-dG-6-P in the determination (see source and incubated at 30 C in a reciprocating below). shaker. Exoenzyme production usually began after a Determination of intracellular hexose-6-phos- delay of 30 to 60 min. The basis of this lag is consid- phate. Washed protoplasts were suspended at 5 x ered below in relation to Fig. 5, which shows a sim- 107 per ml in 0.8 M sorbitol medium with the indi- ilar delay in uptake of 2-dG. To measure enzyme cated concentration of fructose or maltose and incu- released into the medium, 1.0 ml of the incubation bated at 30 C for 40 min. The suspensions were then mixture was withdrawn at intervals and centrifuged centrifuged at 1,000 x g for 3 min. To the pellets at 1,000 x g for 3 min; 0.5 ml of the supernatant was added 2 ml of 7% perchloric acid to stop the fluid was pipetted into 0.5 ml of ice-cold water and reaction and to extract sugar phosphates. Extraction assayed for the enzyme activity. For determination proceeded for 30 min at room temperature, followed of total enzyme synthesis, samples were periodically by neutralization of the samples to pH 7.0 with 0.5 N removed from the mixture and transferred to chilled KOH. After rapid freezing and thawing, protoplast tubes containing ice-cold water to lyse the proto- debris and precipitated KClO, were removed by cen- plasts. trifugation at 3,000 x g at 4 C. The supernatant Enzyme assays. The assays for invertase and fluids were lyophilized and finally suspended in 2 ml alpha-glucosidase were described previously (24). of 0.05 M Tris-hydrochloride buffer (pH 7.6). The 6- Acid and alkaline phosphatases were assayed with p- phosphates of glucose, 2-dG, fructose, and mannose nitrophenyl phosphate (PNPP) as substrate as de- were assayed by NADPH formation in the usual sys- scribed by Torriani (37).
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